Commonly assigned U.S. Pat. Nos. 4,343,754, 4,378,893, 4,418,828, 4,407,422, and 4,497,765 disclose constructions for, and methods and apparatuses for making, composite closures for bottles and like containers. The closures are composite in the sense that they include an outer plastic cap or shell, and a plastic sealing liner positioned adjacent a top wall portion of the plastic cap for effecting sealing engagement with an associated container. By such a construction, the plastic material of the outer cap can be selected to exhibit the requisite strength, while the material for the inner sealing liner can be relatively soft for enhanced sealing with the finish of a container. Significantly, composite closures formed in accordance with the teachings of the above patents have proven highly effective for use on containers having pressurized or carbonated contents, with the above patents further disclosing tamper-indicating closure pilfer band constructions for indicating removal of a closure from a container. Portions of the above patents not inconsistent with the present disclosure are hereby incorporated by reference.
One aspect of the composite closure constructions of the above patents which promotes effective sealing is the formation of the sealing liner with a relatively thick annular sealing bead portion which defines a generally inwardly facing sealing surface. Formation is facilitated by molding the outer plastic cap with an annular liner-retaining lip in closely spaced relation to the top wall portion of the cap, with the annular lip desirably acting to confine the material from which the liner is formed during in situ formation of the liner, preferably in accordance with the compression molding techniques disclosed in the above patents.
While the annular lip acts to retain the liner in position within the cap after formation, liner retention is desirably enhanced by the formation of liner-engaging projections integrally with the top wall portion of the cap. In accordance with the teachings of U.S. Pat. No. 4,407,422 and 4,497,765, formation of a plurality of circumferentially spaced liner-engaging projections extending integrally from the top wall portion in close association with the annular liner-retaining lip desirably acts to mechanically retain the peripheral edge portion of the sealing liner, thus retaining the liner in position. Such circumferentially spaced liner-engaging projections can be partially disposed within the annular recess defined by the annular lip and the top wall portion, and are preferably arranged to engage the relatively thick annular sealing bead portion of the liner.
While the above-described sealing construction has proven effective for use on containers having carbonated contents, experience has shown that enhanced liner retention can be desirable for some applications. As will be appreciated, the liner of a closure is subjected to torsional stresses attendant to application to, removal from, and re-application to a container, and it is generally desirable to avoid dislodgement of the liner when it is subjected to such stresses. While the above-described arrangement of circumferentially spaced liner-engaging projections provides highly effective liner retention with many liner materials, such materials can vary in hardness and like physical characteristics, thus affecting the liner retention characteristics of the liner-engaging projections and annular lip. While increasing the dimensions of the circumferentially spaced liner-engaging projections can act to enhance liner retention, it is desirable that the projections not be so large as to interfere with distribution of the liner material during liner formation, or extend through the liner material after the liner is formed. Accordingly, the present invention concerns an improved liner retaining construction for a composite closure including a plastic cap and a plastic sealing liner.